Branching fraction measurement of the $$ \Lambda \to p{\mu}^{-}{\overline{ u}}_{\mu } $$ decay

A bstract A measurement of the branching fraction for the decay $$ \Lambda \to p{\mu}^{-}{\overline{\nu}}_{\mu } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> <mml:mo>→</mml:mo> <mml:mi>p</mml:mi> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msub> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>μ</mml:mi> </mml:msub> </mml:math> is presented using pp collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. The analysis is based on data recorded between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb − 1 . The result is obtained using Λ → pμ − decays as a normalisation channel. The measured branching fraction is $$ \mathcal{B}\left(\Lambda \to p{\mu}^{-}{\overline{\nu}}_{\mu}\right)=\left(1.462\pm 0.016\pm 0.100\pm 0.011\right)\times {10}^{-4} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>B</mml:mi> <mml:mfenced> <mml:mrow> <mml:mi>Λ</mml:mi> <mml:mo>→</mml:mo> <mml:mi>p</mml:mi> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msub> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>μ</mml:mi> </mml:msub> </mml:mrow> </mml:mfenced> <mml:mo>=</mml:mo> <mml:mfenced> <mml:mrow> <mml:mn>1.462</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.016</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.100</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.011</mml:mn> </mml:mrow> </mml:mfenced> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:math> , where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalisation mode branching fraction, respectively. This result improves the precision of the branching fraction measurement by a factor of two compared to the previous best measurement and sets a more stringent bound on lepton flavour universality in s → u quark transitions. It is consistent with previous measurements, and the extracted lepton flavour universality test observable, $$ {R}^{\mu e}=\frac{\Gamma \left(\Lambda \to p{\mu}^{-}{\overline{\nu}}_{\mu}\right)}{\Gamma \left(\Lambda \to p{e}^{-}{\overline{\nu}}_e\right)}=0.175\pm 0.012 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>R</mml:mi> <mml:mi>μe</mml:mi> </mml:msup> <mml:mo>=</mml:mo> <mml:mfrac> <mml:mrow> <mml:mi>Γ</mml:mi> <mml:mfenced> <mml:mrow> <mml:mi>Λ</mml:mi> <mml:mo>→</mml:mo> <mml:mi>p</mml:mi> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msub> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>μ</mml:mi> </mml:msub> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mi>Γ</mml:mi> <mml:mfenced> <mml:mrow> <mml:mi>Λ</mml:mi> <mml:mo>→</mml:mo> <mml:mi>p</mml:mi> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msub> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>e</mml:mi> </mml:msub> </mml:mrow> </mml:mfenced> </mml:mrow> </mml:mfrac> <mml:mo>=</mml:mo> <mml:mn>0.175</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.012</mml:mn> </mml:math> , agrees with the Standard Model prediction.

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Journal
Journal of High Energy Physics
Published
2026-04-14
DOI
https://doi.org/10.1007/jhep04(2026)096
Primary Topic
Particle physics theoretical and experimental studies
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article
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article

Branching fraction measurement of the $$ \Lambda \to p{\mu}^{-}{\overline{ u}}_{\mu } $$ decay

M. Becker, Sergi Bernet Andres, C. Arata, L. Anderlini et al.
Journal of High Energy Physics
Particle physics theoretical and experimental studies
article

Branching fraction measurement of the $$ \Lambda \to p{\mu}^{-}{\overline{ u}}_{\mu } $$ decay

M. Becker, Sergi Bernet Andres, C. Arata, L. Anderlini, Dong Ao, F. Archilli, S. Arguedas Cuendis
article en

Abstract

A bstract A measurement of the branching fraction for the decay $$ \Lambda \to p{\mu}^{-}{\overline{\nu}}_{\mu } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> <mml:mo>→</mml:mo> <mml:mi>p</mml:mi> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msub> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>μ</mml:mi> </mml:msub> </mml:math> is presented using pp collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. The analysis is based on data recorded between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb − 1 . The result is obtained using Λ → pμ − decays as a normalisation channel. The measured branching fraction is $$ \mathcal{B}\left(\Lambda \to p{\mu}^{-}{\overline{\nu}}_{\mu}\right)=\left(1.462\pm 0.016\pm 0.100\pm 0.011\right)\times {10}^{-4} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>B</mml:mi> <mml:mfenced> <mml:mrow> <mml:mi>Λ</mml:mi> <mml:mo>→</mml:mo> <mml:mi>p</mml:mi> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msub> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>μ</mml:mi> </mml:msub> </mml:mrow> </mml:mfenced> <mml:mo>=</mml:mo> <mml:mfenced> <mml:mrow> <mml:mn>1.462</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.016</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.100</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.011</mml:mn> </mml:mrow> </mml:mfenced> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:math> , where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalisation mode branching fraction, respectively. This result improves the precision of the branching fraction measurement by a factor of two compared to the previous best measurement and sets a more stringent bound on lepton flavour universality in s → u quark transitions. It is consistent with previous measurements, and the extracted lepton flavour universality test observable, $$ {R}^{\mu e}=\frac{\Gamma \left(\Lambda \to p{\mu}^{-}{\overline{\nu}}_{\mu}\right)}{\Gamma \left(\Lambda \to p{e}^{-}{\overline{\nu}}_e\right)}=0.175\pm 0.012 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>R</mml:mi> <mml:mi>μe</mml:mi> </mml:msup> <mml:mo>=</mml:mo> <mml:mfrac> <mml:mrow> <mml:mi>Γ</mml:mi> <mml:mfenced> <mml:mrow> <mml:mi>Λ</mml:mi> <mml:mo>→</mml:mo> <mml:mi>p</mml:mi> <mml:msup> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msub> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>μ</mml:mi> </mml:msub> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mi>Γ</mml:mi> <mml:mfenced> <mml:mrow> <mml:mi>Λ</mml:mi> <mml:mo>→</mml:mo> <mml:mi>p</mml:mi> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:msub> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>e</mml:mi> </mml:msub> </mml:mrow> </mml:mfenced> </mml:mrow> </mml:mfrac> <mml:mo>=</mml:mo> <mml:mn>0.175</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.012</mml:mn> </mml:math> , agrees with the Standard Model prediction.

Journal of High Energy PhysicsVol. 2026(4)
Universidade da Coruña (ES), University of Rome Tor Vergata (IT), Universidade Federal do Rio de Janeiro (BR), University of Modena and Reggio Emilia (IT), Uppsala University (SE), Jagiellonian University (PL), Centre National de la Recherche Scientifique (FR), University of Bonn (DE), École Polytechnique (FR), University of Liverpool (GB), Vilnius University (LT), Taras Shevchenko National University of Kyiv (UA), Université Clermont Auvergne (FR), Universidade de Santiago de Compostela (ES), TU Dortmund University (DE), Peking University (CN), University of Zurich (CH), Aix-Marseille Université (FR), Heidelberg University (DE), University of Cambridge (GB), Pontifícia Universidade Católica do Rio de Janeiro (BR), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris-Saclay (FR), University of Michigan (US), Laboratoire d’Annecy de Physique des Particules (FR), CEA Paris-Saclay - Etablissement de Saclay (FR), Machine Intelligence Research Institute (US), University of Manchester (GB), University of Bristol (GB), University of Warwick (GB), Sorbonne Université (FR), University of Oxford (GB), National Institute for Subatomic Physics (NL), Centre de physique des particules de Marseille (FR), Laboratoire de Physique de Clermont Auvergne (FR), Laboratoire de Physique Nucléaire et de Hautes Énergies (FR), Istituto Nazionale di Fisica Nucleare, Sezione di Padova (IT), Institute of Nuclear Physics, Polish Academy of Sciences (PL), Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara (IT), Istituto Nazionale di Fisica Nucleare, Roma Tor Vergata (IT), FZU ‒ Institute of Physics of the Academy of Sciences of the Czech Republic (CZ), Centro Brasileiro de Pesquisas Físicas (BR), Istituto Nazionale di Fisica Nucleare, Sezione di Genova (IT), CEA Paris-Saclay (FR), Istituto Nazionale di Fisica Nucleare, Sezione di Firenze (IT), Institut National de Physique Nucléaire et de Physique des Particules (FR), Laboratoire de Physique des 2 Infinis Irène Joliot-Curie (FR), Istituto Nazionale di Fisica Nucleare, Sezione di Milano Bicocca (IT), Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati (IT), Istituto Nazionale di Fisica Nucleare, Sezione di Bologna (IT), Laboratoire Leprince-Ringuet (FR), Istituto Nazionale di Fisica Nucleare, Sezione di Roma I (IT), Istituto Nazionale di Fisica Nucleare, Sezione di Pisa (IT), University of Chinese Academy of Sciences (CN), Institut de Recherche sur les Lois Fondamentales de l'Univers (FR), Lamarr Institute for Machine Learning and Artificial Intelligence, Consejo Nacional de Rectores, Imperial College London (GB), École Polytechnique Fédérale de Lausanne (CH), Universitat Ramon Llull (ES), Massachusetts Institute of Technology (US), University of Milano-Bicocca (IT), European Organization for Nuclear Research (CH), AGH University of Krakow (PL), Université Savoie Mont Blanc (FR), Syracuse University (US), Ruhr University Bochum (DE), University of Edinburgh (GB)
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Particle physics theoretical and experimental studies
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